After you file

I am in a similar boat.  Right now I have a return, but the K1 I am expecting this year is from a sale of the assets.  That may change my return to owe taxes.  How can I know what I'll need to pay if I don't have the K1?

I know more or less the gain I got from the sale, I also have some carryover losses from previous years, mostly from accelerated depreciation (cost segregation studies).  I know that depreciation will change my cost basis but I don't know by how much.

So, how can I estimate how much I will owe to the IRS so that I can send  a payment at the same time I file for an extension?